The preparation of flocked articles, wherein flocks are affixed to the surface of a thermoplastic or elastomeric material through an adhesive layer such as a polyurethane, is well known. In such processes, the elastomeric surface is coated with a layer of the adhesive and short staple fibers are applied perpendicularly thereto, often utilizing an electrical field. The resulting electrostatically flocked articles are characterized by a fabriclike surface of relatively low friction. This feature renders flocked articles particularly suitable for the purpose of reducing friction between the sliding glass window and window channel of automobiles, or for enhancing the appearance, utility, and appeal of various pockets and glove boxes found in automotive interiors. In view of the abrasion and stress involved in these applications, it is imperative that the adhesive used to bond the flock to the thermoplastic or elastomeric material contain components which not only bond to the flock, but also bond to the thermoplastic or elastomeric substrate.
One example of a flock adhesive is disclosed in U.S. Pat. No. 4,835,226 and contains an aromatic nitroso compound, an epoxy resin, and an isocyanate functional urethane prepolymer wherein the prepolymer is blocked with a substituted or unsubstituted phenol. Dinitrosobenzene is disclosed as a typical aromatic nitroso compound while epoxy novolak resins are disclosed as typical epoxy resins. Agents for blocking the urethane prepolymer include phenols, and alkyl-substituted phenols such as nonylphenol and cresol.
U.S. Pat. No. 4,535,121 also discloses a flocking adhesive for flexible substrates that contains an isocyanate-terminated polyurethane prepolymer, the reaction product of an aromatic diisocyanate and a polyfunctional epoxide, a solvent, and a dispersant. Typical diisocyanateepoxide reaction products include reaction products of triglycidyl isocyanurate, triglycidyl urazole, diglycidyl benzimidazolone, diglycidyl hydantoin, and condensed glycidyl hydantoins with diphenylmethane diisocyanate, toluene diisocyanate, paraphenylene diisocyanate, and xylene diisocyanate.
While previously developed flock adhesives such as those described above can theoretically be used as a one component preparation, it has been found in practice that in order to obtain maximum bond strength and abrasion resistance from these adhesives, it is necessary to utilize an adhesive primer for the thermoplastic or elastomeric surface. The requirement of a primer to obtain sufficient bond strength and abrasion resistance causes traditional flock adhesive compositions to be undesirable for many industrial applications since it is more efficient and time-saving to utilize a one-component adhesive in order to bond short staple fibers to a substrate.
A need therefore exists for a flock adhesive which can be effectively applied as a one-component composition to rubber or other elastomeric substrates onto which short staple fibers are to be affixed. The one-component composition should also provide high strength adhesive bonds which exhibit substantial abrasion resistance.